(701d) Co-Electrolysis to Achieve Energy Efficient and Economic Conversion of CO2 into Intermediates Such As CO and Ethylene (Invited)

Using CO₂ as a feedstock for the production of intermediates for chemical or fuel production such as formic acid, CO, ethylene, ethanol, and methanol is one of several approaches being explored to help reduce anthropogenic CO₂ emissions, while also reducing society’s dependence on diminishing global fossil fuel reserves. A number of active electrocatalysts for the selective reduction of CO₂ have been reported. For CO production selectivity easily exceeds 95%, and current densities exceeding 200 mA/cm² can be achieved routinely, while overall energy efficiencies are 50-65% [1]. Also, ever more selective catalysts for production of ethylene and/or ethanol are being developed. For example, we recently reported an electrodeposited CuAg alloy catalyst able to produce ethylene and ethanol at a combined selectivity of 85% (3:1 ethylene to ethanol) at a rate of 170 mA/cm² [2]. Techno-economic analyses of these processes indicate that the availability and cost of renewable energy is the most important factor in determining economic feasibility.

After a brief summary of state-of-the-art electrocatalysts for the cathodic reduction of CO₂ to CO and ethylene / ethanol, this talk will focus on exploring anode chemistries to help improve the economics of CO₂ conversion at scale. An analysis of Gibbs free energies indicates that about 90% of the total energy required for CO₂ electrolysis is consumed at the anode for the oxygen evolution reaction. In other words, 90% of the (precious renewable) energy used to drive the process is ‘stored’ in oxygen for which no large market exists. In a quest to find abundantly available chemicals or waste streams that can be electro-oxidized at a much lower potential than water (thus drastically reducing the overall energy requirement of CO₂ electrolysis), we identified glycerol, a large volume by-product of industrial biodiesel and soap production. Using a 2M glycerol solution as the anolyte lowers the overall cell potential by approximately 0.8 V, regardless of the CO₂ electroreduction chemistry on the cathode (CO, formic acid, or ethylene/ethanol formation). The 0.8 V lower cell potential translates to a 45-53% reduction in overall energy requirement, which naturally improves the economics of CO₂ electroreduction. This talk will further elaborate on glycerol oxidation as well as other chemistries that can potentially be used on the anode for economically feasible CO₂ reduction through co-electrolysis approaches.

1. Gold Nanoparticles on Polymer-Wrapped Carbon Nanotubes: An Efficient and Selective Catalyst for the Electroreduction of CO₂, H.R.M. Jhong, C.E. Tornow, C. Kim, S. Verma, J. L. Oberst, P.S. Anderson, A.A. Gewirth, T. Fujigaya, N. Nakashima, P.J.A. Kenis, ChemPhysChem, 2017, 18 (22), 3274-3279.
2. Nanoporous Copper−Silver Alloys by Additive-Controlled Electrodeposition for the Selective Electroreduction of CO₂ to Ethylene and Ethanol, T.T.H. Hoang, S. Verma, S. Ma, T.T. Fister, J. Timoshenko, A.I. Frenkel, P.J.A. Kenis, and A.A. Gewirth, J. Am. Chem. Soc., 2018, accepted.